Internal combustion engines used for vehicles engaged in short run travel (i.e. the so-called stop and go driving) do not reach their most efficient operating temperature. Therefore large amounts of undesirable products produced by incomplete combustion of the fuel and oil-soluble oxidation products from lubricants and other sources accumulate within the internal combustion engine. If these undesirable products deposit on the engine parts, the result is a further reduction of the engine's efficiency. To prevent the accumulation of foreign matter and the deposition of sludge, a dispersant is employed as an additive to the lubricating oil so that the oil-insoluble foreign matter and sludge will remain suspended in the oil and not deposit on any of the vital engine parts.
In addition to the problem of engine deposits, the combustion products of the fuel may cause excessive wear, especially when the engine is operating under relatively cold conditions which results in an accumulation of moisture and acid products on the engine surfaces. This accumulation promotes wear on various engine parts.